Current status

The package is currently in v1.0 stable state, no major issues remain with this version and it should run on a Python 2.7 installation (also works on Enthough Canopy Python).
Standalone packages are available for Windows, Linux and Mac OS X, make sure to get the latest release.
The most up-to-date branch is the "restructuring"-branch, and runs on Windows, Linux and Mac OS X.
A quick start guide and example data is included in the "doc"-directory that comes with the distribution.

Requirements

To run McSAS from the source code repository (i.e. using a Python interpreter), the following items are required:

Installation on systems with a working Python distribution

For those unfamiliar with the Git versioning system, it is recommended to start by installing Altassian SourceTree (and perhaps reading Bitbucket 101 ).
This is a GUI around the Git versioning system that simplifies the usage and allows you to get started quickly.

Using the "clone" button on the top left side of this page, you can download a copy of the latest version.
Make sure when downloading to select the "restructuring"-branch.
Following this, McSAS can be started on Unix(-like) systems by opening a terminal window, changing directory to the location of McSAS, and typing

$ ./main.py

On Windows systems, double-clicking the "main.py" file should open python and start McSAS.

Standalone packages

Standalone packages are available in the downloads section of this page.
These are available for Mac OS X (tested on 10.6, 10.8 and 10.10), Windows and Linux.
These do not require any additional software to be installed on the host computer.